The invention relates to an inverter having first and second switches connected in series across a DC source. When one of the switches is conducting, the other is open.
Care must be taken given such an inverter known from German OS No. 31 12 281, incorporated herein by reference, that alternately activated electronic switches never, and not even briefly, conduct current at the same time which would result in a short-circuit of the constant voltage source. Observation of this condition is particularly important given employment of semiconductor switches. Given an inverter of the type initially cited, therefore, the operating frequency of the inverter during ignition mode determined for example by a saturation transformer, is therefore placed above a resonant frequency of a series oscillating circuit. The inverter is then inductively loaded and the current through a switch employed in the inverter necessarily becomes zero before the voltage passes through zero and, dependent thereon, another switch employed in the inverter is driven.
A variety of causes, such as the failure of one or more lamps or an unfavorable coincidence of the tolerances of components, can result in the operating frequency of the inverter closely approaching the resonant frequency. Given, in particular, very low loss components of the series oscillating circuit, this consequently leads to correspondingly high voltages which can jeopardize not only the components of the inverter, but also can result in danger to personnel when they work at the lamp sockets.